In welding processes, wherein a consumable wire forms the electrode and supplies the filler metal, there is often a problem with feeding the wire. Where the distance between the wire reel or spool and the arc is reasonably short, and where the wire has good column strength, the wire feed problem is minimized. However, in many welding applications, wire is removed from a wire reel or reservoir and fed into the arc welding operation at a point which is a considerable distance from the wire reel. In traversing the path extending from the wire reel to the arc, the wire is sometimes passed through wire guides of one form or another such as eyes, conduit, or hollow flexible cables, which may or may not be lined with a friction reducing liner. In many cases, this can be done without too much difficulty but in other cases there are problems. For example, where the distance between the wire reel and the arc is large, or where there are significant bends in the wire guide, it becomes necessary to use a "pusher" system near the wire reel to pull the wire from the wire reel and push the wire into the wire guide, and a "puller" system near the arc, typically in the welding gun, to pull the wire from the wire guide and feed the wire to the arc welding operation.
Where the wire is pushed, it may collapse as a column, jam in the wire guide, wrap around the drive rolls, or cause the drive rolls to slip with respect to the wire, thus stalling the wire feed or causing the wire to feed in an erratic manner. Where serrated rolls are used, slippage of the drive rolls with respect to the wire may cause the drive rolls to mill the wire. Where the wire is pulled, excessive drag in the wire guide may cause the wire to break from the tension, slip or stall the wire feed system, or cause the rolls to mill the wire. These problems are further aggravated where a small diameter wire is used, especially where soft wire such as aluminum wire is used or where bends in the wire guide cause excessive friction.
The pusher system and the puller system should both feed at the same rate. If the pusher system attempts to feed wire at a higher rate than the puller system attempts to pull the wire the wire may collapse in the wire guide, may wrap around the drive rolls, or cause the drive rolls to slip, thereby galling or milling the wire. If the puller system is faster than the pusher system the tension may be excessive and cause the wire to break or the drive rolls on one or both of the systems may slip. If the drive rolls slip the wire may alternately feed at the speed of the pusher system and then at the speed of the puller system. The problem is further aggravated if any attempt is made to vary the wire feed speed because it is very difficult to match the speeds of the two drive systems over any appreciable range.
To avoid this problem some prior systems use a speed adjustable motor for one system and a constant torque motor for the other system. Such a wire feeder is described in U.S. Pat. No. 3,293,477.
However, it is still found that the wire may occasionally collapse as a column, jam in the wire guide, wrap around the feed rolls, or slip with respect to the drive rolls. This occurs when the tip in the welding gun as jammed so that the wire cannot feed from the welding gun. This problem happens more frequently with soft, small diameter wire, such as aluminum.
Five conditions create the majority of jamming problems. First, the wire can burn back and weld itself to the end of the tip. Second, fine weld splatter can splash back out of a welding puddle and can clog the outlet of the tip and restrict the wire feed. Eventually, the diameter of the hole of the tip becomes reduced from the splatter to the point where the wire stops feeding or at least encounters a substantial amount of friction. Third, as a result of wire going through the wire guide and being pushed or pulled through the mechanism and various openings, small wire shavings form, especially when knurled or serrated rollers are used. The movement of the wire draws the shavings and powder into the tip and, eventually, a wedge may form inside the tip which substantially increases the friction of the wire going through the tip or may stop the wire entirely. Fourth, a poor electrical contact between the tip and the wire may cause the wire to melt inside the tip. This melted area may then immediately resolidify inside the tip, bind to the tip, and prevent the wire from coming out. Fifth, a form of etching or corrosion can take place inside the tip due to current transfer between the tip and the wire. Material is pulled from the tip, the wire, or both, to produce particles which build up inside the tip and restrict or reduce the size of the opening in the tip.
If any of these conditions occur then, when the welding operator next pulls the trigger, the pusher and puller systems will attempt to feed the wire. If the puller system is not a limited torque system then the wire may deform and spool out inside the welding gun. If the driver is not a limited torque system then the wire may collapse in the wire guide, jam in the wire guide, and/or spool out into the pusher mechanism. Although collapsing or jamming of the wire is a problem in and of itself, the spooling of the wire into the various mechanisms is a major problem because the welding operator must then take the time to cut and pull the wire out of the mechanism, thereby wasting a substantial amount of time.
When the trigger is pulled, the wire may feed out of the welding gun at a rapid rate if there is any slack in the wire. This can cause the wire to feed at a high rate until the slack is taken out. The wire can strike the workpiece, causing a high striking current which can cause burn-through of thin material, stubbing if there is insufficient power to strike the arc, or wire burn-through, which can cause the arc to strike and burn back to the tip.
Therefore, there is a need for a wire feeder which properly feeds wire to a welding operation but does not feed wire when a blockage occurs.
There is also a need for a method of adjusting a wire feeder so that the wire feeder will properly feed wire to a welding operation but will not feed wire when a blockage occurs.
There is also a need for a wire feeder which will maintain the wire in tension at all times.